Fouling – an annoying problem in the wort kettle

To heat a liquid, you need a heating surface, which must have a higher temperature in order to transfer the heat to the liquid.

There are two important issues: the temperature difference between the heating surface and the liquid and the size of the heating surface. The greater the temperature difference, the more heat can be transferred, and the larger the heating surface, the more can be transferred.

But there is also a third factor: the dynamic factor of the liquid to be heated, i.e. whether it is in motion or not. A liquid at rest has a high heat accumulation on the heating surface and transfers this heat only slowly to zones further away.

This is where the coefficient of thermal conductivity and viscosity would come into play, but let’s leave that aside, otherwise it will get too complicated.

If the factors of heating surface temperature, heating surface size and dynamic factor are unfavourably correlated, i.e. the heating surface temperature is too high in relation to the liquid temperature, the heating surface is too small and the liquid is at rest, then tiny solids in the wort will adhere to the heating surface, forming a film that builds up ever faster and eventually can no longer be removed with CIP cleaning.

This complicated explanation can also be described as “soup burns”.

With water there is also a deposit along the heating surface, usually it is the limescale in the water, but never as intense as with wort.

With mash, however, the dynamic factor plays a major role; a resting mash will burn very quickly once the boiling temperature has been reached.

Directly fired kettles are an absolute no-go, as the heating surface is too small and the temperature too high and drag chains mounted on the agitator to scrub away burnt mash are no help.

Another no-go are electric heating elements in direct contact with mash or wort.

The larger the heating surface and the smaller the temperature difference between the heating surface temperature and the liquid while simultaneously mixing the liquid, the less fouling will occur.

On the subject of mixing with an agitator, there are numerous scientific papers on the design of a perfect agitator blade.

SALM doesn’t have heated kettles. SALM has an external mash and wort boiler, optionally heated by a gas burner, by steam or thermoelectrically.

The brewing product is circulated between the kettle and the boiler with the aid of a special pump, whereby only a spiral-shaped tube (in case of the fired version) or a coaxial tube is used. The speed is set so that the wall flow corresponds to the flow in the tube axis.

During the subsequent brew, the husks of the mash polish the tube wall, thus keeping it clean. Furthermore, the heat supply is set in a way to prevent overheating and the temperature difference between the liquid inlet and outlet never exceeds 4.5°C.

Discover SALM’s smart brewing technology: our external boiler systems for maximum efficiency and hygiene in the brewing process.

Contact SALM for a non-binding consultation and find out how to optimize your brewing process and brew at the highest level.